It is known that acetylene can be polymerized with a catalyst to yield polyacetylene, a structure comprising a chain of carbon atoms connected by alternating single and double bonds with hydrogen atoms in both the cis and trans configurations.
The use of catalysts such as a conventional Ziegler-Natta catalyst, used at relatively low concentrations, leads to the production of an amorphous mass of polyacetylene. Shirakawa et al., described a method for producing coherent films of polyacetylene using the so-called Ziegler-Natta catalyst. [Polymer J., Volume 2, p. 231 (1971)].
Leiser et al., described the use of a modified Luttinger's catalyst to produce coherent films of polyacetylene. [Makromol, Chem. Rapid Commun., Volume 1, p. 621 (1980)]. Twenty milligrams of NaBH.sub.4 were dissolved in 50 mL of ethanol and 50 mL diethyl ether were added. The resulting colorless solution was cooled to -80.degree. C., and 1 mL of a 1% by weight solution of Co(NO.sub.3).sub.2 in ethanol was added to form a catalyst solution. A support such as a glass slide was dipped into the catalyst solution and transferred rapidly into an atmosphere of acetylene. These investigators report that as soon as the thin liquid layer of catalyst solution is exposed to acetylene, polymerization commences and the whole slide becomes covered with a coherent layer of cis-polyacetylene within a few seconds of exposure at -30.degree. C.
The polyacetylene films were floated off the glass slide onto a water surface. In the hands of the present inventor, the films produced by this method were not coherent upon drying. The films were fragile gels that crenated badly upon drying. Attempts to wash the gels--necessary to remove catalyst components--prior to drying were disastrous in that the gels broke, were washed off the slide or were completely disrupted.
Monkenbusch et al., describe a similar procedure. These investigators emphasize that polymerization begins as the support is allowed to warm up. [Makromol. Chem. Rapid Commun., Volume 3, p. 69 (1982)].
Edwards et al., report that as the polymerization reaction mixture is allowed to warm up from about -78.degree. C. to about -25.degree. C., the evolution of gas is observed. These investigators presumed that the gas was hydrogen, produced by the decomposition of the borohydride catalyst. [Makromol. Chem. Rapid Commun. Volume 4, p. 393 (1983)].
As reported by Edwards et al., the increase in temperature from about -80.degree. C. to about -30.degree. C., which is required by the prior art to produce coherent films of polyacetylene, causes the production of gas which, in turn, has a serious tendency to disrupt the structural integrity of the polyacetylene films. The prior art suggests no way of raising the temperature in a controlled way to avoid the formation of this disruptive gas.
As would be suggested to those skilled in the art by Edwards et al. who used rigorously dried reagents and who carried out polymerization under a nitrogen atmosphere, it is also important to avoid the presence of water during the polymerization process.
Shirakawa et al. used a catalyst comprising a mixture of titanium tetrabutoxide and triethylaluminium in a solvent. It is known that both of these compounds are extremely reactive with water and oxygen necessitating dry and inert reaction conditions.
Surprisingly, it has been discovered that extremely coherent films of polyacetylene can be produced if the catalyst contains water and an acidic component. Excellent quality coherent films of polyacetylene, strongly adherent to the support on which they are formed, are produced by this novel and unexpected process. In addition, the use of water and an acidic component permits the entire process to be carried out at a single temperature of about -80.degree. C.